The proposed research will be directed towards the study of two potentially important modulators of myocardial and vascular contractility-cyclic GMP dependent protein kinase (cGPK) and the cyclic AMP dependent protein kinase inhibitor (PKI). This will include purification and characterization of cGPK from heart and smooth muscle, determination of its mechanism of action and assessment of its possible role in cardiovascular disease. It will also extend current research on PKI, the goal being the elucidation of its physiologic role.